The present invention relates to a printer having an auxiliary pin tractor unit in addition to a main pin tractor unit in which the auxiliary pin tractor unit is detachably mounted on the upper portion of the main pin tractor unit provided interiorly of a printer housing. The invention further relates to a printer having a changeover means for the selectively driving the two pin tractors with a single drive source.
A conventional printer includes a single pin tractor for supplying a continuous sheet and a sheet feed roller for supplying cut sheets. The printer further includes a transmission means for selectively transmitting rotations of a motor to the sheet feed roller and the pin tractor so that the latter two are driven with a single motor. Alternatively, a switching means is provided which, while constantly rotating the sheet feed roller, performs on/off switchings of the rotations of the pin tractor, wherein the rotations of the pin tractor are halted when the cut sheets are being supplied.
In such conventional printers, the cut sheets and the continuous sheet are available. However, it may be desirable to use another type of continuous sheet, different from the continuous sheet loaded on the pin tractor, depending upon the purpose of the printing. In such a case, the continuous sheet would need to be replaced with another one.
To this end, sheet replacement work has to be carried out in a manner such that: a sheet urging member urging the loaded continuous sheet is raised, the loaded continuous sheet is removed from the pin tractor to replace it with another continuous sheet by engaging perforations formed along the side marginal portions of the contiguous sheet with the pins of the pin tractor, and then the sheet urging member is laid down. When alternately using different kinds of continuous sheets, the sheet replacement work must be done very often.
Selective use of the two kinds of the continuous sheets may be possible if two pin tractors are installed in the printer. If this were done, the intricate sheet replacement work could be dispensed with. However, when it is desired to use still another kind of the continuous sheet which is different from those loaded in the two pin tractors, sheet replacement work must be done anyway. In addition, in order to perform the sheet replacement work, a working space needs to be provided near the place where the pin tractors are installed. Due to the structural limitations of the printer, however, a sufficient space cannot be reserved. Furthermore, if the two pin tractors are driven with a single motor. Either one of the two pin tractors must be selectively driven and both of the pin tractors must be halted at a time. A mechanism for changing over the driving between the sheet feed roller and a single pin tractor as used in the conventional printers is not available for the purpose of implementing the three-mode drive control.
The above and other problems remain unsolved and thus printers having two pin tractors have not yet been produced.